Tectonic Deformation Characteristics And Uplift Process During Cenozoic In The Bogda Mountain Chains Of The Eastern Tianshan Mountains

As an inner plate orogenic belt,Tianshan Mountain experienced the subduction collision in Paleozoic.In the Cenozoic,under the influence of the collision of the early India Eurasia plate and the northward pushing after that,it was subjected to strong compression and uplift of structural deformation,and it formed a regenerated orogenic belt within the continent.Clarifying the characteristics of Cenozoic tectonic deformation in the Tianshan Mountains is of great significance for understanding the deformation mechanism of the orogenic belt in the mainland.As an important branch of the Tianshan Mountains,the Bogda mountain chain has become a hot topic in the study of geotectonics and continental dynamics in recent years.In this paper,through field structural analysis and apatite fission track research,we can distinguish the Cenozoic structural deformation characteristics and uplift process of the Bogda mountain chain.The thrust faults and folds of Bogda mountain chain constitute thrust nappe structure.By using the method of stereographic projection,the dominant direction of the folds is NNE direction,which is formed in the compression environment near north-south.The profile shows that the strata on the north side of the mountain thrust from the south to the north,and the strata on the south side thrust from the north to the south.The two sides of the mountain form a fan-shaped structural pattern.On the basis of Paleozoic and Mesozoic deformation,the Cenozoic underwent more intense deformation and formed the present structural characteristics.The apatite fission track shows a single peak distribution in length and age of single particle,indicating that it is controlled by a single thermal event.The average uplift rate of the sample was 0.057mm/a by the age-closed temperature method.Based on the apatite fission track data published before,the statistical results show that there are four relatively rapid uplifting stages in the Bogda orogenic belt since the Cretaceous: 105-110 Ma,80-95 Ma,55-65 Ma,15-30 Ma,among which the Oligocene-Miocene uplifting reached its peak.At the same time,the uplifting is different in space.In the east-west direction,the west is earlier than the east.In the north-south direction,the southern side was earlier than the northern side in the late Cretaceous and the north side is earlier than the south side in the Cenozoic.The uplift of Bogda orogenic belt is related to the collision between India-Eurasian plate,and the two-way accumulation of deep materials.Under the action of North-South two-way compression,a fold thrust belt is formed from the middle of the mountain to the North-South sides.The strike slip fault developed in the mountain and the fold thrust belt developed towards the basin form a typical compression and torsion orogenic system.Orogenic belts and basins on both sides form a "rhombic symmetry" pattern.